Lead-lined digester



(No Model.)

S. SMITH. LEAD LINBD DIGESTBR.

Noe 428,149. Patented May 2o, 1890.

MATNEEEEE- No., wAsHmG'mN, n. c.

UNITED STATES PATENT OFFICE.

SIDEr SMITH, OF CAMBRIDGE, MASSACHUSETTS.

LEAD-LINED DIGESTER.

SPECIFICATION forming part of Letters Patent No. 428,149, dated May 20,1890.

Application filed April 9, 1889. Serial No. 308,591. (No model.)

To all whom it may concern.:

Be it known that I, SIDNEY SMITH, of Cambridge, in the county ofMiddlesex and Stat-e of Massachusetts, have invented certain new anduseful Improvements in Lead-Lined Digesters, of which the following is aspecification.

This invention has for its object the construction of a boiler, eitherupright or lhorizontal, which is heated either by a suitable furnace orby the int-roduction of steam produced in a separate boiler. The boilerconstitutes what is known in the manufacture of paper from wood or anyvegetable iiber as a digestein The proper vegetable fiber is boiled orcooked in such digester with some suitable solvent agent capable ofcompletely freeing the fiber from all incrusting` substances, like gumsand resins. In all casos where this solvent agent is liable to attackthe metal of which the digester is coniposed it is necessary tointerpose between the solvent agent and the metallic walls of the digestel' some Inedium in itself unaffected by the solvent agent whichshall protect the dig-ester from solvent action during the process ofcooking. lVhenever lead has been used for a protecting medium or liningfor an iron or steel digester, it has been found that the lead issubject to so Inuch wear and tear, owing to the extremes of temperature,that it is a matter of great expense and annoyance to keep the lining inproper condition.

In practice the lining of sheet-lead is held in place against the ironor steel shell by a great variety of fastenings, and as the coeflicientsof expansion of lead and iron are widely different, and as they are bothheated through a wide range of temperature, the lead finds no outlet forits excess of eXp-ansion over .that of the iron, and the result isconstantly repeated-folding or buckling of the lead and an equivalentracking strain upon the iron shell. Cracks and holes are thus producedin the lead, while the iron is dangerously weakened. To provide for thefree expansion of the lead is the object of my invention.

The shell of my digester is best made of iron or steel plates solidlybuttwelded by electricity in such a manner as to produce one homogeneouspiece composing the boiler; but the sheets may be butted nearly togetherand both edges beveled, so as to form a slight open dovetailed joint,and bound together by a band of steel or iron, which covers the joint onthe outside of the boiler and is riveted to both plates. The opendovetailed joint is then to be fitted with lead or any substance knownto withstand the liquid contents ofthe boiler. By such a joint aperfectly smooth interior to the boiler is produced. Said joint isdescribed and claimed in another application filed concurrentlyherewith.

The cylindrical shell is made larger at one end than at the other, andaccordingly has a true taper externally throughout its entire length.The lead lining is made either of sheet-lead fitted and solderedtogether on the interior surface or the lead is melted and poured intothe space between the boiler, and

a suitable form let down into the boiler-shell,

of a size such that the lead casting or lining thus produced shall be ofthe desired thickness and entirely cover the bottom and sides of theboiler. If the lining is made of sheets, the latter can be fitted andjoined in the boiler, or may be fitted together outside and then letdown into the boiler. The latter proceedin g is facilitated by the tapershape of the boiler.

One end of the boiler is provided with an expansion-joint analogous tothe joint of the same name in steam-pipes. Upon the lead lining, whichreaches nearly to the head of the digester, rests a Inovable circularhead, which is tightly packed between the lead and itself by asbestus orany suitable substance known to resist the chemical action of the liquorin the digester. The space between the two head s-viz.,the outerortruehead and the movable inner headmay receive steani,or may be providedwith springs or other means for exerting a holding-down yieldingpressure upon the movable head. The movable head constitutes a pistonworking against a regulated resistance and adapted to rise and fall asthe lead lining expands or contracts. Further- Inore, owing to thetapering form of the digester, which is larger at the end provided withthe expansion-joint, expansion from all parts of the digcster tends toiind a relief or outlet IOC at this end. Both. of the heads mentionedmay be provided with man-holes `for the introduction of stock, tbc., andthe digester is iitted with all gages, valves, and connections necessaryfor safety and for determining the condition of the contents during thecooking.

In the accompanying drawings, forming a part of this specification,Figure l represents a vertical section of my improved digester andasetting or casin g therefor. Fi 2 represents an enlarged section ot aportion of the digester.

The same letters of reference indicate the same parts in all thefigures.

In the drawings, ct represents the outer shell of the digester, which ispreferably of cylindrical form and tapers or increases gradually indiameter from its lower to its upper end, said shell being made of steelor iron plates suitably connected.

I) represents the lead lining, which is formed to ht the interior of thedigester and extends nearly but not entirely to the top ot the same, itsupper end being open. A space c exists between the upper end of thelining and the upper end or head a ot the digcster. In said space islitted the movable head or piston d, which. bears on a packing c, ofasbestus or other acid-resisting material, interposed between the saidhead and the upper end of the lead lining, and constitutes averticallymovable cover for said lining. I make the portion of the outershell which projects above the lining of uniform diameter, instead oftapering, like the major portion of the digester, so that the verticalmovements of the movable head will not aiii'ect the closeness of itscontact with the inner surface of the digester, it being desirable thatthe movable head fit the interior of the outer shell at all times. Themovable head has a sufficiently close bearing on the packing c at thcupper end of the lining to prevent the escape ot' liquid therefrom intothe space c, and this bearing is maintained by a constan t downwardyielding pressure which is exerted on the movable head. I prefer toexert said pressure by steam introduced into the space c through a pipei, the pressure of said steam being regulated by a reducing-valve orotherwise, so that it will permit the head (Z and the upper end ot thelining to rise and fall by expansion and contraction ot the liningwithout permitting the head to be forced oit from the lining by theinternal pressure.

Instead ot' steam as the means for applying yielding pressure to themovable head, I may employ a spring or springs for the same purpose.

The digester may be heated externally or may be heated internally bysteam or other suitable medium. I have here shown the digester inclosedin a casing or setting 7.?, having Y(lues 911, through which theproducts of combustion pass along the external suri'aces of the digesterfrom a furnace o. 'ihcdigester should have the usual accessories, suchas a gage-tube, safety-valve, rbc. The outer head u. is detachalilysecured, and may have a manhole r, which coincides with another man-holeinthe movable inner head, said man-holes enabling the digester to becharged and emptied.

I claiml. A digester-body or outer shell of tapering form, having aeorrespoiidingly-taperiug lining resting on the inner surtaceot theouter shell without positive connection therewith.

2. The combination of a digester-body or outer shell, an openmouthedlead lining placed therein without positive connection therewith, and amovable head or piston bearing on the upper end or mouth et the lining,as set forth.

3. The combination ot a dgester-body or outer shell, an open-mouthedlead lining therein without positive connection therewith, a movablehead or piston bcarii'ig on the upper vend or mouth of the lining, andmeans ior holding the piston against the end ot the lining with ayielding pressure, as set forth. In testimony whereof I have signed myname to this specification, in the presence of two subscribingwitnesses, this 2d day ot' April, A. l). ISSU.

SIDNEY SMITH. `\\'itnesses:

C. F. BnowN, A. D. HARRISON.

